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Hydrology: Groundwater and Wells

Lane Cockrell, Southwestern Travis County GCD
LMUD Open House presentation, October 19, 2023

Lakeway MUD is a surface-water supplier, pulling our raw water exclusively from Lake Travis. However, all water is connected (aquifers feed springs and creeks that become our rivers and lakes) so we invited Lane Cockrell, a hydrogeologist and general manager for the Southwestern Travis County Groundwater Conservation District (GCD) to present at our open house about the challenges facing the groundwater supply in our area.

Surface water and groundwater are managed differently in Texas

as though they exited in silos even though they are inherently linked, so understanding how groundwater can contribute to lake water levels and vice versa, especially in drought conditions, is very important. With more water management districts, we are able to build more connected protection and management policies, ideally based on watershed boundaries, rather than municipal boundaries.

Groundwater Conservation Districts (GCDs) have been around since 1949 when they were declared by the Texas Legislature as the State’s preferred means to manage groundwater resources through its protection, preservation, and conservation utilizing the best available science. Groundwater is sourced from underground aquifers and can be extracted using a water well. In Texas, where private property rights are sacred, property owners have a right to produce groundwater from beneath their property (drill a well) as long as they can demonstrate a need for it and will put it to “beneficial” use. Since GCDs are not permitted to regulate development, one key focus is outreach and education to help reverse groundwater depletion. Through data gathering and evaluation, GCDs also provide a more effective voice in managing groundwater as a resource for future generations through better informed future policies.

Groundwater is and will continue to be a major source of water in Texas. While potable (drinking) water is thought to be a limitless resource, in many parts of the state, the amount of groundwater being used is outpacing how much is being replenished through natural means. GCDs aim to reverse this trend, however it’s a difficult task with continuous population growth, leading to “too many straws drinking from the same glass.” In our area, this population growth is especially focused around the Interstate-35 corridor which is supplied by the Trinity Aquifer. Made up by three zones: the Lower Trinity, Middle Trinity, and Upper Trinity, the majority of Southwestern Travis County GCD’s (SWTCGCD) service area falls in the Lower Trinity, which is the deepest of the three aquifers. Data collection on water-level changes in the Lower Trinity Aquifer from Spring 1978 to Fall 2018 show over 200 feet of drawdown in areas with concentrated pumping, including the Lakeway and Bee Caves area. Additional data from the Texas Water Development Board shows a decline of two to three feet per year since the 1950s.

Through strategically placed monitoring wells, we are able to see hour-by-hour and seasonal use data points throughout the Trinity Aquifer. For example, in one subdivision that is entirely dependent on groundwater, in the morning, when everyone is taking showers, we see daily quick, temporary declines in water level as well as seasonally in late summer to early fall, when everyone is irrigating. There is a chance for some recovery over the winter when water use declines.

We know a lot more than we did even just a few years ago due to ongoing data collection, but there is still a lot to be discovered to better understand and manage groundwater as a resource. This includes effectively mapping the geology of the area: the characteristics of the rocks and the structure (such as a fault zone) impact how groundwater flows, impeding some areas and flowing to others. If you are interested in learning more, we have scientific publications of geophysical and hydrogeologic studies available on our website: swtcgcd.com/groundwater-studies.